1. Field of Invention
The invention relates to a fin and tube heat exchanger including end plates and a series of spaced parallel fins arranged therebetween that are provided with apertures which accommodate the tubes with the tube end portions extending through the end plates with connectors joined thereto, and more particularly to the method of replacing defective end portions of the tubes.
2. Description of the Prior Art
Many heat exchange coils are now constructed with a large number of aluminum "U" tubes extending transversely through holes in aluminum fins. After the assembly of the tubes to the fins, the tubes are then expanded outwardly to seat tightly against the fin material defining the holes in which the tubes are situated. The open ends of the tubes extending through the fins are expanded and dimensioned to receive connectors. Then, aluminum return bend connectors and other fittings such as tripods, crossovers, and various headers are placed on the open ends of the tubes and the heat exchanger is subjected to an operation in which these fittings are permanently joined to the tube ends by means of solder or adhesive.
Several differing types of soldering operations may be used, such as flame preheat/ultrasonic solder bath dip and flame preheat with suitable flux and solder alloy in which some of the joints may become sufficiently hot that one or more return bends or other fittings may be effectively destroyed or damaged along with the bell end of the tube in which the fitting is located. Furthermore, these same parts may be exposed to sufficiently intense ultrasonic energy that they may be effectively destroyed due to cavitation erosion. This problem can arise because different fittings present different heat transfer and ultrasonic energy problems so that while one setting may be quite proper for one type of joint, it may be incorrect for another particular joint and damage to the tube ends and fittings may result. Further, defects in the tube end portions, such as pin holes, splits, cracks, partial melt downs, etc. that are caused when the end portion and tubes are worked on before and/or after the main soldering operation can also cause leaks which would render the heat exchanger useless for employment in a sealed refrigeration system.
Irrespective of the cause, a tube which has its end damaged must either be repaired or the entire coil scrapped. Since the coils include substantial material in the form of tubes, fins, and fittings, as well as labor cost invested therein, scrapping of the coils is very costly.
In some prior art, approaches to repairing the coil and the tubes, including the defective portion, are removed. One way which has been employed for removing tubes is to slit the wall of the tube longitudinally by a device that is pushed through the tubes. Another way is to cut a helix in the tube wall the length of the tube and then pulling the tube out by collapsing the helix on itself.
In the type of heat exchanger with which the present invention is concerned, the tube is expanded outwardly throughout its total length to seat tightly in the apertures of each of the fins and plates through which the tube passes. This type heat exchanger requires that the expanded tube be relieved from its contact with all of the apertures along its entire length. This requires highly specialized tools and skill on the part of the repair person to insure that the apertures from which the tube was removed are left in such condition that the tube can be replaced and the coils salvaged. This procedure is further complicated in that typically tubes having a U-shaped configuration are employed which necessitate the removal of both legs of the U-shaped tube.